In the field of paper machine belts in particular, felt belts are known in which a support made up of textile plastic yarns is embedded in a fiber matrix of plastic fibers. Paper machine belts of this kind are used chiefly as press felts in the press section of a paper machine. The fiber matrix is manufactured in such a way that one or more nonwoven fabric layers are needle-felted onto the support on one or both sides.
In the felt belt of the species, the support is made up not of a woven fabric but of at least two yarn layers arranged one above another. A yarn layer has yarns that are arranged in parallel fashion at a distance from one another and that, unlike in woven and knitted fabrics, are not engaged into one another. The yarn layers are arranged so that the yarns of adjacent yarn layers intersect, generally in such a way that one yarn layer is embodied as a longitudinal yarn layer having longitudinal yarns extending in the longitudinal direction of the felt belt, and one yarn layer is embodied as a transverse yarn layer having transverse yarns proceeding in the transverse direction.
A felt belt of this kind in the form of an endless press felt is disclosed in U.S. Pat. No. 4,781,967. For manufacture of the felt belt, firstly modules are formed that are made up either entirely of a fiber layer or of a combination of fiber layer and yarn layer. Regarding the manufacture of these modules, the reader is referred to U.S. Pat. No. 3,613,258. The individual modules are then laid onto one another and joined to one another without the use of binding yarns, in part using extruded polymer material. The manner in which an endless felt belt results from the joining of the individual modules is not evident from U.S. Pat. No. 4,781,967.
Because hot-melt adhesive fibers or adhesive is used, the press felts according to U.S. Pat. No. 4,781,967 are relatively dense (cf. U.S. Pat. No. 6,425,985 B1, col. 1, lines 38 to 47) and stiff. This limits the usability of such felt belts in paper machines.
EP 1 359 251 A1 likewise discloses a support made up of at least two yarn layers arranged one above another, in which context the support can also be covered with a fiber layer. Manufacture of the support proceeds in such a way that the longitudinal yarns are stretched parallel to one another between two yarn beams, and the transverse yarns are then laid over the longitudinal yarns. The transverse yarns are then fused to the longitudinal yarns by being heated (in a manner confined to their intersection points) to melting temperature. Heating of the yarns can be accomplished by means of a laser beam when the yarns are equipped with an additive that promotes absorption of the laser beam.
Although a highly dimensionally stable support is obtained with this method, a prerequisite therefore is that the longitudinal and transverse yarns abut one another in planar fashion, which requires a specific yarn shape. This yarn shape in turn conflicts with embedding of the support into a fiber matrix by means of needle-felting of nonwoven fabric layers. Such supports are therefore of only limited suitability for the manufacture of press felts, and are intended chiefly for use in the dryer section of a paper machine, and in that case without a fiber layer or fiber matrix.
EP 0 464 258 A1 describes a method for manufacturing a felt belt, in particular as a press felt, in which the support is built up by the fact that a support web strip whose width is substantially less than the intended width of the support is wound in helical or screw-shaped fashion onto two spaced-apart rollers until the intended width of the support is reached. Simultaneously or subsequently, the support is covered in the same way with nonwoven fabric strips, and the nonwoven fabric web thus formed is needle-felted to the support. The oblique side edges of a felt belt constructed in this fashion are then trimmed so as to yield straight side edges that extend in the machine direction.
With this manner of manufacturing the support, the longitudinal yarns extend, because of the winding process, at an angle to the longitudinal direction of the felt belt, and continuous transverse yarns are not obtained, so that the transverse strength of the felt belt is not very high. In order to obtain better transverse strength, it has been proposed to join the edges of the support web strips to one another, for example by stitching (U.S. Pat. No. 5,360,656). In the context of supports manufactured from yarn layers, the edges of the support web strips are, according to EP 0 947 623 A1, joined to one another by the fact that the transverse yarns of the transverse yarn layer engage into one another at the edges, and a joining yarn is laid on there and is welded to the portions of the transverse yarns that interengage. This has the disadvantage, however, that in the region of the edges a strip is created that, because of the differing arrangement and density of the yarns, has properties that are different from those of the other surfaces of the felt belt, in particular lower permeability. This can result in marks on the paper.
To remedy this, it is proposed in EP 1 209 283 A1 to embody the edges of the support web strips in meander fashion with successive projections and indentations, and to abut the support web strips against one another in such a way that the projections and indentations interengage, such that the projections completely fill the indentations. The edges are then joined via joining means, for example stitched seams or adhesive strips. This too, however, results in changes in the properties of the completed felt belt in the region of the interengaging edges.